Disturbance Observer Based Contact Detection for Motorized Hydraulic Actuators

Contact detection without endpoint tactile sensing is challenging; friction and inertia obscure the sensing of low amplitude and high frequency forces. In this work we explore fluidic transmissions as series-elastic actuators, coupled to remotely-located direct-drive brushless motors, in a bid to maximize low-impedance sensitivity to contact while maintaining high bandwidth. We employ a disturbance observer to remove motor friction and further reduce minimum impedance. Using a 2-DOF remotely-actuated hydraulically-coupled robotic gripper, we demonstrate a maximum endpoint Z-width of 40dB and a robust contact detection threshold of 0.2N, without endpoint tactile sensing or joint position sensing. These results enable wiring-free and joint sensor-free arm and end-effector design, which are of particular interest for human-robot interaction, harsh-environment, magnetically-sensitive, and low-cost robotic manipulators that must maintain high bandwidth and high contact sensitivity.